NAME

       phc2sys - synchronize two or more clocks

SYNOPSIS

       phc2sys -a [ -r ] [ -r ] [ options ]
       phc2sys [ -d pps-device ] [ -s device ] [ -c device ] [ -O offset ] [ -w ] [ options ]

DESCRIPTION

       phc2sys  is  a  program  which  synchronizes  two  or more clocks in the system. Typically, it is used to
       synchronize the system clock to a PTP hardware clock (PHC), which itself is synchronized by the  ptp4l(8)
       program.

       With the -a option, the clocks to synchronize are fetched from the running ptp4l daemon and the direction
       of synchronization automatically follows changes of the PTP port states.

       Manual  configuration  is  also  possible. When using manual configuration, two synchronization modes are
       supported, one uses a pulse per second (PPS) signal provided by the source clock and the other mode reads
       time from the source clock directly. Some clocks  can  be  used  in  both  modes,  the  mode  which  will
       synchronize the slave clock with better accuracy depends on hardware and driver implementation.

OPTIONS

       -a     Read the clocks to synchronize from running ptp4l and follow changes in the port states, adjusting
              the   synchronization   direction   automatically.   The  system  clock  (CLOCK_REALTIME)  is  not
              synchronized, unless the -r option is also specified.

       -r     Only valid together with the -a option. Instructs phc2sys to also  synchronize  the  system  clock
              (CLOCK_REALTIME). By default, the system clock is not considered as a possible time source. If you
              want the system clock to be eligible to become a time source, specify the -r option twice.

       -d pps-device
              Specify  the  PPS  device  of  the  master  clock  (e.g.  /dev/pps0).  With  this  option  the PPS
              synchronization mode is used instead of the direct mode. As the PPS signal does not  specify  time
              and  only  marks  start  of  a second, the slave clock should be already close to the correct time
              before phc2sys is started or the -s option should be used too. With the -s option the  PPS  signal
              of  the  master  clock  is enabled automatically, otherwise it has to be enabled before phc2sys is
              started (e.g. by running echo 1 > /sys/class/ptp/ptp0/pps_enable).  This option can be  used  only
              with the system clock as the slave clock. Not compatible with the -a option.

       -s device
              Specify  the  master  clock  by  device (e.g. /dev/ptp0) or interface (e.g. eth0) or by name (e.g.
              CLOCK_REALTIME for the system clock). When this option is used together with the  -d  option,  the
              master  clock is used only to correct the offset by whole number of seconds, which cannot be fixed
              with PPS alone. Not compatible with the -a option.

       -i interface
              Performs the exact same function as -s for compatibility reasons.  Previously  enabled  specifying
              master  clock  by  network interface. However, this can now be done using -s and this option is no
              longer necessary. As such it has been deprecated, and should no longer be used.

       -c device
              Specify the slave clock by device (e.g. /dev/ptp1) or interface  (e.g.  eth1)  or  by   name.  The
              default is CLOCK_REALTIME (the system clock). Not compatible with the -a option.

       -E servo
              Specify  which  clock servo should be used. Valid values are pi for a PI controller, linreg for an
              adaptive controller using linear regression, and ntpshm for the NTP SHM reference clock  to  allow
              another process to synchronize the local clock.  The default is pi.

       -P kp  Specify the proportional constant of the PI controller. The default is 0.7.

       -I ki  Specify the integral constant of the PI controller. The default is 0.3.

       -S step
              Specify  the  step  threshold  of  the  servo. It is the maximum offset that the servo corrects by
              changing the clock frequency instead of  stepping  the  clock.  The  clock  is  stepped  on  start
              regardless  of  the  option  if the offset is larger than 20 microseconds (unless the -F option is
              used). It's specified in seconds. The value of 0.0 disables stepping after the start. The  default
              is 0.0.

       -F step
              Specify  the  step  threshold  applied  only on the first update. It is the maximum offset that is
              corrected by adjusting clock. It's specified in seconds. The value of  0.0  disables  stepping  on
              start.  The default is 0.00002 (20 microseconds).

       -R update-rate
              Specify  the  slave clock update rate when running in the direct synchronization mode. The default
              is 1 per second.

       -N phc-num
              Specify the number of master clock readings per one slave clock update. Only the  fastest  reading
              is used to update the slave clock, this is useful to minimize the error caused by random delays in
              scheduling and bus utilization.  The default is 5.

       -O offset
              Specify  the  offset  between  the  slave  and master times in seconds. Not compatible with the -a
              option.  See TIME SCALE USAGE below.

       -L freq-limit
              The maximum allowed frequency offset between uncorrected clock and the system monotonic  clock  in
              parts  per  billion (ppb). This is used as a sanity check of the synchronized clock. When a larger
              offset is measured, a warning message will be printed and the servo will be reset. When set to  0,
              the sanity check is disabled. The default is 200000000 (20%).

       -M segment
              The number of the SHM segment used by ntpshm servo.  The default is 0.

       -u summary-updates
              Specify  the number of clock updates included in summary statistics. The statistics include offset
              root mean square (RMS), maximum absolute offset, frequency offset mean and standard deviation, and
              mean of the delay in clock readings and standard deviation. The units are  nanoseconds  and  parts
              per  billion  (ppb).  If  zero,  the individual samples are printed instead of the statistics. The
              messages are printed at the LOG_INFO level.  The default is 0 (disabled).

       -w     Wait until ptp4l is in a synchronized state. If the -O option is not used, also  keep  the  offset
              between  the  slave and master times updated according to the currentUtcOffset value obtained from
              ptp4l and the direction of the clock synchronization. Not compatible with the -a option.

       -n domain-number
              Specify the domain number used by ptp4l. The default is 0.

       -x     When a leap second is announced, don't apply it in the kernel by stepping the clock, but  let  the
              servo  correct  the one-second offset slowly by changing the clock frequency (unless the -S option
              is used).

       -z uds-address
              Specifies the address of the server's UNIX domain socket.  The default is /var/run/ptp4l.

       -l print-level
              Set the maximum syslog level of messages which should be printed or sent to the system logger. The
              default is 6 (LOG_INFO).

       -m     Print messages to the standard output.

       -q     Don't send messages to the system logger.

       -h     Display a help message.

       -v     Prints the software version and exits.

TIME SCALE USAGE

       Ptp4l uses either PTP time scale or UTC (Coordinated Universal Time)  time  scale.   PTP  time  scale  is
       continuous  and  shifted  against  UTC  by  a  few  tens of seconds as PTP time scale does not apply leap
       seconds.

       In hardware time stamping mode, ptp4l announces use of PTP time scale and PHC is  used  for  the  stamps.
       That  means PHC must follow PTP time scale while system clock follows UTC.  Time offset between these two
       is maintained by phc2sys.

       Phc2sys acquires the offset value either by reading it from ptp4l when -a or -w  is  in  effect  or  from
       command  line  when  -O  is  supplied.  Failure to maintain the correct offset can result in local system
       clock being off some seconds to domain master system clock when in  slave  mode,  or  incorect  PTP  time
       announced to the network in case the host is the domain master.

EXAMPLES

       Synchronize  time automatically according to the current ptp4l state, synchronize the system clock to the
       remote master.

              phc2sys -a -r

       Same as above, but when the host becomes the domain master, synchronize time in the domain to its  system
       clock.

              phc2sys -a -rr

       The  host  is  a domain master, PTP clock is synchronized to system clock and the time offset is obtained
       from ptp4l.  Phc2sys waits for ptp4l to get at least one port in master or slave mode before starting the
       synchronization.

              phc2sys -c /dev/ptp0 -s CLOCK_REALTIME -w

       Same as above, time offset is provided on command line and phc2sys does not wait for ptp4l.

              phc2sys -c /dev/ptp0 -s CLOCK_REALTIME -O 35

       The host is in slave mode, system clock is synchronized from PTP clock, phc2sys waits for ptp4l  and  the
       offset is set automatically.

              phc2sys -s /dev/ptp0 -w

       Same  as  above,  PTP clock id is read from the network interface, the offset is provided on command line
       phc2sys does not wait.

              phc2sys -s eth0 -O -35

SEE ALSO

       ptp4l(8)

linuxptp                                          November 2012                                       PHC2SYS(8)